Cobalah sendiri - Google Maps ref

<!DOCTYPE html>
<html>
<head>
<script
src="/lib/google-map-api.js">
</script>

<script>
var map;
function initialize()
{
var mapOpt = {
  center:new google.maps.LatLng(51.508742,-0.120850),
  zoom:6,
  mapTypeId:google.maps.MapTypeId.ROADMAP
  };
map=new google.maps.Map(document.getElementById("googleMap"),mapOpt);
}

google.maps.event.addDomListener(window, 'load',initialize);
</script>
</head>
<body>

<button onclick="alert(map.getBounds());">Get bounds</button>
<br><br>
<div id="googleMap"style="width:400px;height:300px;"></div>

</body>
</html>